1. Field of the Invention
This invention relates generally to the field of pumping systems for raising fluids from wells. More particularly, the invention relates to a novel technique for directing fluid from one element of a submergible pumping system, such as a fluid separator, to another element of the pumping system, such as a production pump. The technique facilitates channeling of the fluid displaced by the pumping system.
2. Description of the Related Art
In producing petroleum and other useful fluids from production wells, it is generally known to provide a submergible pumping system for raising the fluids collected in a well. In general, production fluids will enter a well via perforations formed in the well casing adjacent to a production formation. The fluids contained the formation will then collect in the wellbore and may be raised by the pumping system to a collection point above the earth's surface. In many instances, non-production fluids may also accumulate in the wellbore. Such non-production fluids may include water, brine and other fluids of less commercial interest.
Known pumping systems for raising production fluids from wells typically include a submergible electric motor coupled to a production pump. The electric motor is supplied with electrical power via a cable extending to power supply and control circuitry above the earth's surface. The production pump draws in production fluids and forces the production fluids to the earth's surface via a conduit, such as a stand of coil tubing. Where wellbore fluids include a significant quantity of non-production fluids, the pumping system may include a separator for separating the production fluids from the non-production fluids. The non-production fluids may be reinjected into a subterranean discharge or disposal zone either directly from the separator or via a separate injection pump. The injection pump may also be driven by the same electric motor used to drive the production pump.
Depending upon the relative positions of the production and discharge zones in the well, various configurations of the components described above may be employed. For example, a separator may be positioned below the electric motor used to drive the production pump. Production fluid output from the separator must then be channeled upwardly in the pumping system from the separator production outlet to the intake of the production pump. In general, it is preferable to channel at least a portion of the fluids displaced by the pumping system adjacent to the electric motor so as to convectively cool the electric motor by the fluid flow. Shrouds may be employed in such situations to channel fluids in annular regions between the shrouds and the outer periphery of the pumping system. The use of such shrouds also facilitates the piping of the pumping system by reducing the need to provide separate fluid conduits between the system components.
In submergible pumping systems employing shrouds for directing fluids between system components, a difficulty arises in making necessary electrical connections with the submergible electric motor. In particular, a shroud is most effective in aiding to cool the electric motor when it is installed to extend at least partially along the outer surface of the motor. However, an electrical connection must be made between the power supply and control cable and the electric motor to power the motor during operation of the system. The cable may be brought through a continuous shroud and sealed at a point of entry through the shroud wall. However, the resulting structure is relatively difficult to assembly and may result in leakage into or out of the shroud during use. Alternatively, packers may be employed between the pumping system and the well casing to eliminate the need for a shroud. However, this arrangement generally requires that the electrical cable be passed through at least one packer to the electric motor. In another solution, a lower shroud portion may be provided around the electric motor, and an upper shroud portion provided to the production pump inlet, with a separate external conduit coupled to both shroud portions. However, this structure also may be prone to leakage and somewhat defeats the purpose of reducing space requirements by virtue of the shroud.
There is a need, therefore, for an improved technique for directing fluids in a submergible pumping system which addresses and at least partially overcomes the drawbacks and disadvantages of existing systems. In particular, there is a need for an improved arrangement for directing fluids around a submergible electric motor and to the inlet of a submergible pump, while permitting electrical connection to be completed between surface equipment and the electric motor via a cable.